The use of radiotherapy in the treatment of cancer is based on the fact that ionizing radiation inhibits the proliferative capacity of tissues and results in cell death. The objective of this proposed work is to study the effects of ionizing radiation on the biochemical events which occur during the cell cycle and are involved in cell proliferation. Since it has been shown that the non-histone chromosomal proteins may be involved in DNA replication, cell division and the regulation of gene expression, the response of this biochemical fraction to ionizing radiation would add important insight to the understanding of radiation-induced defects in cell kinetics. The long term goal will be to evaluate techniques, such as the use of hyperthermia, to distrupt the normal sequences of biochemical events controlling cell proliferation in order to improve radiation therapy of malignant disease.